It is well known to provide an agricultural harvester with a non-contact sensor disposed adjacent a crop material feed tube for determining a crop material characteristic such as, for example, crop moisture content and/or crop density, as the crop material is being conveyed through the feed tube by an auger. The sensor may be an RF microwave sensor as disclosed by Hamid and Stuchly in the publication IEEE Transactions on Industrial Electronics and Control Instrumentation, Vol. IECI-22, May, 1975, or a capacitance or inductance sensor as disclosed in U.S. Pat. No. 5,092,819 to Schroeder et al.
In order to develop an accurate indication of the crop material characteristics being measured, these sensors require a constant packing density of the crop material as it moves through a sensing region. Schroeder et al. teaches the use of a broken flight auger, that is, an auger with a flighting section of reduced diameter in the sensing region, to obtain a more uniform packing. In the case of RF microwave sensors, it is conventional to provide a broken flight auger with that portion of the auger flighting which would otherwise extend through the sensing region entirely removed. This not only avoids modulation of the sensing signal by the rotating flighting but also produces a more uniform packing density of the crop material in the sensing region.
When a broken flight auger is used, the auger flight section upstream of the sensing region conveys the crop material into the sensing region where it accumulates until the sensing region is filled to some level which, for a given crop material, is dependent on the inclination of the feed tube at the sensing region. Thereafter, as more crop material is conveyed into the sensing region by the upstream flighting, it forces crop material out of the sensing region and into the auger flight section, if any, downstream of the sensing region. The crop material in the sensing region is thus packed to a density that is more uniform than would exist if the crop material was conveyed through the sensing region by unbroken flighting.
As long as the feed tube is inclined upwardly in the downstream direction by about 20.degree. or more relative to horizontal, the broken flight auger results in a packing density which is sufficiently constant to permit reasonably accurate sensing of the crop material characteristics. However, when the feed tube is horizontal, inclined downwardly in the downstream direction, or inclined upwardly by less than about 20.degree., the packing density of the crop material in the sensing region will vary sufficiently to result in inaccurate measurements of the characteristics.
The problem of maintaining a constant packing density also exists in other applications, such as in a laboratory test apparatus or a measurement apparatus in a grain storage elevator. In these applications the non-contact sensor is disposed adjacent a vertically oriented feed tube and the crop material is permitted to fall through the feed tube and sensing region under the force of gravity. As the crop material falls, it does not distribute uniformly across the width of the tube. It tends to fall in clusters and even within these clusters the material is not uniformly distributed.
A prior art solution to the problem has been to provide a funnel or fixed flow restrictor located downstream of the sensing region so that the crop material backs up and fills the sensing region. While this arrangement may be suitable for a laboratory test apparatus, it is not suitable for use in harvesters. Since the flow restrictor is fixed, it can not be varied to accommodate different crop flow rates as are encountered when harvesting a field having some areas where the crop is thick and other areas where the crop is light or thin. The flow restrictor must be chosen such that it causes crop to back up into the sensing region even when harvesting the lightest crop. The restrictor thus unduly limits the crop flow rate when areas of thick crop are being harvested.